September 11 WTC Attack Simulations
Using LS-Dyna

Phase III, as of September 10, 2006


Mete A. Sozen, Ayhan Irfanoglu, Christoph M. Hoffmann


The Larger Team and Responsibilities


Project Conception Mete Sozen, Civil Engineering
Project Direction Christoph Hoffmann, Computer Science, CRI
Simulation Setups Ayhan Irfanoglu, Civil Engineering
Oscar Ardila-Giraldo, Civil Engineering
Ingo Brachmann, Civil Engineering

Computing Infrastructure Support

Information Technology at Purdue
Rosen Center for Advanced Computation
Bowen Civil Engineering Laboratory
Northwest Indiana Computational Grid
Network for Computational Nanotechnology

Project Funding   NSF-ITR DSC-0325227, A. Sameh, PI
Mesh Generation
Post Processing
Christoph Hoffmann, Computer Science
Paul Rosen, Computer Science
Engineering Models Ayhan Irfanoglu, Civil Engineering
Oscar Ardila-Giraldo, Civil Engineering
Ingo Brachmann, Civil Engineering

                                 Scientific Supervision

Mete Sozen, Civil Engineering

Supercomputer Runs Paul Rosen, Computer Science


Voicu Popescu, Computer Science

Physical Experiments

Santiago Pujol, Civil Engineering

Graduate Students Oscar Ardila-Giraldo, Civil Engineering
Ingo Brachmann, Civil Engineering
Tyler Krahn, Civil Engineering
Paul Rosen, Computer Science


Problem Statement

Simulate as faithfully as possible the effects of crashing an air frame loaded with fuel (simulating a Boeing 767-200ER) into a steel and concrete structure similar to the structure of the WTC-1, North Tower, of the World Trade Center. 

Purpose of the Effort

Use the simulation results to understand what the extent of damage done by the impact has been.  Effects of the subsequent fire are not under consideration in this phase of the project.

Use the simulation results also to construct animations and visualizations that vividly reenact of the impact, as it plausibly has been.  This work will be Phase IV.


The fully configured impact simulations are runs 11 and 12.  Earlier runs calibrated and refined the simulation setup.

The modeled airframe is loaded with the approximate amount of fuel and set to impact the WTC-1 building (the North Tower) at the speed, position and orientation published in official reports.  Both the exterior building skeleton and the core support structure of the building have been modeled, as well as the concrete floors and supporting girders.

Simulation Parameters

The simulation uses adaptive time stepping which averages to approximately 0.000001 sec time steps.  We generate snapshots of the simulation approximately every 0.0025 sec.  The airplane arrives with an initial velocity of 470 mph.  Penetration to the core structure of the building takes approximately 0.1 sec.  

Animations and Stills

Simulation Animations and Stills Problem Size
Compute Time
North Tower
Simulation Run 11
327 K 100 hours,
8 processors,
0.5 sec
North Tower
Simulation Run 12
327 K 30 hours,
16 processors,
0.37 sec


Calibrations and Experiments

The aircraft model was constructed from publicly available data.  The FEA model has been calibrated by computing mass distributions and evaluating the Riera curve.

From our modeling of the aircraft crash into the Pentagon building, we knew that a critical issue in defining the damage was the modeling of the fuel in the aircraft.  Much of the mass of the aircraft is provided by the fuel; in this case about 27%.  The energy imparted to the impacted structure is the initial cause of the damage.  This time, we modeled the fluid-structure interaction using smooth particle hydrodynamics (SPH).  To calibrate our approach, Dr. Pujol built a special test setup that made it possible to hurl 6-oz liquid containers at a steel target of varying speeds approaching 100 m/sec. 


This work has been supported in part by NSF ITR grant DSC-0325227; the PI of the grant is Dr. Sameh, the NSF officer is Frederica Derema.  For the work of the larger ITR project see the project website.

Infrastructure support for the large-scale simulations has been provided by the Northwest Indiana Computational Grid (NWICG), and by Purdue's Network for Computational Nanotechnology (NCN).


A. Irfanoglu and C. Hoffmann, "An Engineering Perspective of the Collapse of WTC-1," J. of Performance of Constructed Facilities, ASCE, 06/2007; in press.

Last updated July 17, 2007